Something else that’s very interesting is that the highest percentage of apps in the App Store are now paid book applications. In total, there are over 27,000 book apps in the store, and of those 92% are paid apps, according to Distimo’s data. That number bodes very well for Apple’s soon-to-be-released iPad, of which a big selling point will be the new iBooks application.

A lot of those, of course aren't book "apps" as much as "a book with built in reader", and very few are $14.99, or even $9.99. Or $4.99.